A display device such as a liquid crystal device has been conventionally and widely used in apparatus such as a cellular phone and a projector. A liquid crystal display device having a TFT (Thin Film Transistor) includes a TFT substrate and a facing substrate, which are pasted to each other, and has liquid crystal sealed between the substrates. In general, the examination for checking whether a manufactured liquid crystal device is performed on the finished product. For example, a predetermined image signal may be input to, projected to and displayed on the liquid crystal device as display data so that whether the data can be displayed correctly and the presence of any lacking pixel can be checked.
However, the method of examining a finished product is not preferable from the viewpoint of management of manufacturing steps. This is because the detection of a poor product is delayed since the poor product is detected after the steps of manufacturing the substrate.
This increases the time taken for feeding back the detection of a poor product to the step management. As a result, the period with a low yield increases, which also increases the manufacturing cost. Also in prototyping, in since the period from the evaluation of a prototype to the feedback to the design process increases, which may increase the development period and the development costs. Furthermore, the repair of a poor point is difficult after the product is finished.
Accordingly, a poor point, especially, a lacking pixel in a display device is desirably detected within steps of manufacturing the substrate.
One of such examining methods proposed is a technology for examining a liquid crystal display device by bringing an examination probe in contact with an electrode pad of a liquid crystal display device and supplying a predetermined amount of current thereto (see Patent Document 1, for example). Furthermore, another technology is proposed for applying a predetermined amount of voltage to each pixel on a TFT substrate in consideration of the capacitor characteristic of pixels and examining the function of the TFT based on waveforms of the discharged current and discharged voltage (see Patent Document 2, for example).
Furthermore, another technology is proposed for examining an operation of each pixel electrode by detecting an amount of potential change of a pixel electrode on the TFT substrate by using an opposed electrode for examination corresponding to the pixel electrode (see Patent Document 3, for example).
[Patent Document 1]: Japanese Unexamined Patent Application Publication No. 5-341302;
[Patent Document 2]: Japanese Unexamined Patent Application Publication No. 7-333278; and
[Patent Document 3]; Japanese Unexamined Patent Application Publication No. 10-104563